MIMO DSP in Direct Detection SDM Systems Based on Weakly-Coupled Multicore Fibers

This paper explores a new class of space-division-multiplexing (SDM) optical communication links based on weakly-coupled multicore fibers (WC-MCF). These links achieve higher capacity by utilizing WC-MCFs with denser packing of fiber cores. The increased core density leads to significant intercore crosstalk (ICXT), which can no longer be neglected as in WC-MCF links but can be mitigated by a multiple-input-multiple-output (MIMO) digital signal processing (DSP) algorithm. We conducted a numerical study of a passive optical network (PON) link of this new class, which uses a 20 km 8 -core WC-MCF. Our findings show that, when the total ICXT strength is moderate, the MIMO time-domain equalizer (TDE) applied after direct detection (DD) is capable of reducing the mean bit-error ratio (BER) by 1.2 to 2.4 times. Moreover, MIMO TDE significantly lowers the BER in rare but impactful strong-ICXT events that produce high BERs, thus, enhancing the overall link performance and stability.